Organic light emitting diode

ABSTRACT

The present specification discloses an organic electroluminescent device including: an anode; a cathode; a light emitting layer provided between the anode and the cathode; and a light scattering layer provided between the light emitting layer and the cathode.

TECHNICAL FIELD

The present description relates to an organic electroluminescent device.

This application claims priority from Korean Patent Application No.10-2012-0058936, filed on May 31, 2012, at the KIPO, the disclosure ofwhich is incorporated herein by reference in its entirety.

BACKGROUND ART

An organic electroluminescent device converts a current into visiblelight by injecting electrons and holes from two electrodes into anorganic material layer. The organic electroluminescent device may have amultilayer structure including two or more organic material layers. Forexample, the organic electroluminescent device may further include anelectron or hole injection layer, an electron or hole blocking layer, oran electron or hole transporting layer, if necessary, in addition to alight emitting layer.

Recently, as the use of the organic electroluminescent device has beendiversified, studies on materials, which may improve the performance ofthe organic electroluminescent device, have been actively conducted.

DETAILED DESCRIPTION OF THE INVENTION Technical Problem

The present specification describes an organic electroluminescent devicehaving a novel structure.

Technical Solution

An organic electroluminescent device according to an exemplaryembodiment of the present specification includes: an anode; a cathode;and a light emitting layer provided between the anode and the cathode;and further includes a light scattering layer provided between the lightemitting layer and the cathode.

According to another exemplary embodiment of the present specification,the organic electroluminescent device includes: a first electric chargetransporting passage provided between the light emitting layer and thecathode; and a second electric charge transporting passage providedbetween the light emitting layer and the anode,

in which the first electric charge transporting passage includes: afirst p-type organic material layer associated with the cathode; and afirst n-type organic material layer provided between the first p-typeorganic material layer and the light emitting layer, and

the light scattering layer is the first p-type organic material layer,or is provided between the first p-type organic material layer and thefirst n-type organic material layer.

According to still another exemplary embodiment of the presentspecification, the organic electroluminescent device includes: a bufferlayer provided between the light emitting layer and the cathode,

in which the buffer layer includes: a first p-type organic materiallayer associated with the cathode; and a first n-type organic materiallayer provided between the first p-type organic material layer and thelight emitting layer, and

the light scattering layer is the first p-type organic material layer,or is provided between the first p-type organic material layer and thefirst n-type organic material layer.

According to yet another exemplary embodiment of the presentspecification, the organic electroluminescent device includes: a firstp-type organic material layer provided between the light emitting layerand the cathode; and a first n-type organic material layer providedbetween the light emitting layer and the first p-type organic materiallayer, and

the light scattering layer is the first p-type organic material layer,or is provided between the first p-type organic material layer and thefirst n-type organic material layer.

Advantageous Effects

Exemplary embodiments according to the present specification may improvelight extraction efficiency by changing the passage of light generatedin the device by the light scattering layer.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1 to 3 illustrate stacked structures of organic material layers oforganic electroluminescent devices according to exemplary embodiments ofthe present specification, respectively.

FIG. 4 illustrates a movement of an electric charge between a firstp-type organic material layer and a cathode in the organicelectroluminescent devices illustrated in FIGS. 2 and 3.

FIG. 5 illustrates a movement of electric charges among a light emittinglayer, a first n-type organic material layer, the first p-type organicmaterial layer, and the cathode in the organic electroluminescent deviceillustrated in FIG. 3.

FIGS. 6 and 7 illustrate a movement of electric charges among a lightemitting layer, a first n-type organic material layer, a first p-typeorganic material layer, and a cathode in organic electroluminescentdevices according to other exemplary embodiments of the presentspecification.

FIGS. 8 and 9 illustrate a movement of electric charges between an anodeand a cathode in organic electroluminescent devices according to otherexemplary embodiments of the present invention.

FIGS. 10A to 10F are SEM photographs illustrating surfacecharacteristics of light scattering layers manufactured in ExperimentalExamples.

FIGS. 11A to 11C are SEM photographs illustrating surfacecharacteristics of organic material layers formed in the ExperimentalExamples.

BEST MODE

Hereinafter, exemplary embodiments exemplified in the presentspecification will be described in detail.

In the present specification, an n-type means n-type semiconductorcharacteristics. In other words, an n-type organic material layer is anorganic material layer having a characteristic that electrons areinjected or transported at the LUMO energy level, and an organicmaterial layer having a characteristic of a material having an electronmobility greater than a hole mobility. Conversely, a p-type means p-typesemiconductor characteristics. In other words, a p-type organic materiallayer is an organic material layer having a characteristic that holesare injected or transported at the highest occupied molecular orbital(HOMO) energy level, and an organic material layer having acharacteristic of a material having a hole mobility greater than anelectron mobility. In the present specification, “an organic materiallayer which transports electric charges at the HOMO energy level” andthe p-type organic material layer may be used as having the samemeaning. Further, “an organic material layer which transports electriccharges at the LUMO energy level” and the n-type organic material layermay be used as having the same meaning.

In the present specification, an energy level means a size of energy.Accordingly, even when an energy level is expressed in a negative (−)direction from a vacuum level, the energy level is interpreted to meanan absolute value of the corresponding energy value. For example, theHOMO energy level means a distance from the vacuum level to the highestoccupied molecular orbital. In addition, the LUMO energy level means adistance from the vacuum level to the lowest unoccupied molecularorbital.

In the present specification, an electric charge means an electron or ahole.

In the present specification, “an electric charge transporting passage”means a passage through which electrons or holes are transported. Thepassage may be formed at the interlayer interface, and may be formedthrough an additional layer. For example, a first electric chargetransporting passage in the exemplary embodiment includes a first p-typeorganic material layer and a first n-type organic material layer.Furthermore, in the exemplary embodiment, a second electric chargetransporting passage may include only an interface between an anode anda light emitting layer, and may include a layer additionally providedbetween the anode and the light emitting layer.

In the present specification, “non-doped” means that an organic materialconstituting an organic material layer is not doped with a materialhaving other properties. For example, when a “non-doped” organicmaterial layer is a p-type material, the “non-doped” may mean that theorganic material layer is not doped with an n-type material. Further,the “non-doped” may mean that a p-type organic material is not dopedwith an inorganic material other than an organic material. Since organicmaterials having the same properties, for example, p-typecharacteristics are similar to each other in terms of properties, thetwo or more thereof may be mixed and used. The non-doped organicmaterial layer means that the layer is composed of only materials havingthe same characteristics in properties thereof.

According to an exemplary embodiment of the present specification,provided is an organic electroluminescent device including: an anode; acathode; a light emitting layer provided between the anode and thecathode; and a light scattering layer provided between the lightemitting layer and the cathode. FIG. 1 illustrates a stacked structureof a layer in the organic electroluminescent device according to anexemplary embodiment of the present specification. According to FIG. 1,the anode, the light emitting layer, the light scattering layer, and thecathode are stacked on a substrate.

The light scattering layer may include a light scattering structureprovided in or on the surface of the layer.

According to an exemplary embodiment of the present specification, thelight scattering structure may be formed by a particle structure formedby constituting a cluster of molecules of a material included in thelight scattering layer. Here, the particle structure includes anindividual particle formed by constituting a cluster of molecules or astructure formed by agglomerating these particles. Here, the structureformed by agglomerating particles means the at least a part of thesurface or backbone of each of the particles maintains a form beforebeing agglomerated. Accordingly, roughness is produced in or on asurface of a light scattering layer by the agglomerated structure whilethe structure of individual particles or particles is(are) maintainingthe form of at least a part of the surface or backbone before beingagglomerated.

For example, a degree of roughness caused by a particle structure formedby constituting a cluster of molecules of a material included in thelight scattering layer may be from 2 nm to 50 nm. Here, the degree ofroughness is an Ra value in atomic force microscope (AFM) data. Here,the Ra is calculated by an average value of differences between surfaceheights on the surface having roughness.

According to the exemplary embodiment, light extraction efficiency bylight scattering may be maximized by providing a light scattering layerhaving roughness according to the aforementioned particle structurebetween the cathode and the light emitting layer. Specifically, lightemitting efficiency may be maximized by minimizing light absorptionaccording to a surface plasma. In addition, when the light scatteringlayer is associated with the cathode and one or more organic materiallayers are provided between the light scattering layer and the lightemitting layer, thickness uniformity of the organic material layer maybe achieved and deterioration in device efficiency may be prevented,compared to the case of including a light scattering structure in thelight emitting layer or the organic material layer which is in contactwith the light emitting layer.

According to an exemplary embodiment of the present specification, thematerial included in the light scattering layer is an organic material.In other words, a light scattering function may be imparted by roughnessaccording to the particle structure formed by constituting a cluster oforganic material particles.

The organic material of a specific type may have a particle structurehaving roughness as described above only by forming a layer by adeposition method.

The particle structure may be formed by depositing two or more materialsat a specific component ratio, and a particle structure having theaforementioned roughness may also be formed by only depositing even onematerial by intrinsic physical properties of the material.

Depending on the type of material included in the light scatteringlayer, a size of particles formed by constituting a cluster of particlesof a material when the light scattering layer is formed may be varied.For example, a particle diameter of particles formed by constituting acluster of molecules of the material included in the light scatteringlayer may be several micron, for example, in a range from 0.5 micrometerto 30 micrometers, specifically, from 1 micron to 10 micron. Theabove-described roughness may be controlled according to the particlediameter of particles. In order to control the particle diameter of theparticle, it is possible to select the type of material and thecombination or the combination ratio of materials for forming the lightscattering layer.

Even depending on the thickness of the light scattering layer, the sizeor roughness of particle formed by constituting a cluster of moleculesof the material included in the light scattering layer may be varied.The thickness of the light scattering layer may be selected by the typeof material or process conditions, and the light scattering layer may beformed to have a thickness, for example, from 20 nm to 500, andspecifically, from 50 nm to 200 nm.

According to another exemplary embodiment of the present specification,the light scattering layer is provided to be in physical contact withthe cathode. At this time, the surface which is in contact with thelight scattering layer of the cathode may have a form of the particlestructure having roughness on the surface which is in contact with thecathode of the light scattering layer. According to an example, even asurface opposite to the surface which is in contact with the lightscattering layer of the cathode may have a form of a particle structurehaving roughness on a surface which is in contact with the cathode ofthe light scattering layer.

According to still another exemplary embodiment of the presentinvention, the organic electroluminescent device includes: a firstelectric charge transporting passage provided between the light emittinglayer and the cathode; and a second electric charge transporting passageprovided between the light emitting layer and the anode, in which thefirst electric charge transporting passage includes: a first p-typeorganic material layer associated with the cathode; and a first n-typeorganic material layer provided between the first p-type organicmaterial layer and the light emitting layer, and the light scatteringlayer is the first p-type organic material layer, or is provided betweenthe first p-type organic material layer and the first n-type organicmaterial layer.

According to yet another exemplary embodiment of the present invention,the organic electroluminescent device includes: a buffer layer providedbetween the light emitting layer and the cathode, in which the bufferlayer is associated with the cathode and includes: a first p-typeorganic material layer; and a first n-type organic material layerprovided between the first p-type organic material layer and the lightemitting layer, and the light scattering layer is the first p-typeorganic material layer, or is provided between the first p-type organicmaterial layer and the first n-type organic material layer.

According to still yet another exemplary embodiment of the presentinvention, the organic electroluminescent device includes: a firstp-type organic material layer provided between the light emitting layerand the cathode; and a first n-type organic material layer providedbetween the light emitting layer and the first p-type organic materiallayer, in which the light scattering layer is the first p-type organicmaterial layer, or is provided between the first p-type organic materiallayer and the first n-type organic material layer.

When the light scattering layer is provided between the first p-typeorganic material layer and the first n-type organic material layer, itis possible to simultaneously exhibit effects to be described below bythe light scattering layer and the first p-type organic material layer,and the first p-type organic material layer may improve adhesioncharacteristic between the light scattering layer and the cathode. FIG.2 illustrates an example of the organic electroluminescent deviceexhibiting the effects.

According to FIG. 2, an anode, a light emitting layer, a first n-typeorganic material layer, a light scattering layer, a first p-type organicmaterial layer, and a cathode are sequentially stacked on a substrate.FIG. 2 illustrates an example in which the anode is provided on thesubstrate, but the case where the cathode is provided on the substrateis also included in a range of the present exemplary embodiment. Forexample, the organic electroluminescent device according to an exemplaryembodiment of the present specification may have a structure in whichthe cathode, the first p-type organic material layer, the lightscattering layer, the first n-type organic material layer, the lightemitting layer, and the anode are sequentially stacked on the substrate.

When the light scattering layer is the first p-type organic materiallayer, it is possible to simultaneously exhibit an effect caused byintroducing the first p-type organic material layer by introducing onelayer, and an effect caused by the light scattering layer. FIG. 3illustrates an example of the organic electroluminescent deviceexhibiting the effects.

As an example, the light scattering layer may include a polycycliccondensed ring compound and an aryl amine compound. The light scatteringlayer including a polycyclic condensed ring compound and an aryl aminecompound may be the first p-type organic material layer, or may beprovided between the first p-type organic material layer and the n-typeorganic material layer.

An example of the aryl amine compound includes a compound of thefollowing Formula 1:

In Formula 1, Ar₁, Ar₂, and Ar₃ are each independently hydrogen or ahydrocarbon group. At this time, at least one of Ar₁, Ar₂, and Ar₃ mayinclude an aromatic hydrocarbon substitute, and substitutes may be thesame as each other, and may be composed of different substitutes. Thosewhich are not an aromatic hydrocarbon among Ar₁, Ar₂, and Ar₃ may behydrogen; a straight, branched, or cyclic aromatic hydrocarbon; and aheterocyclic group including N, O, S, or Se.

Ar₁ to Ar₃ may be unsubstituted or substituted with alkyl, aryl,heteroaryl, or arylamine. The alkyl includes a C₁ to C₂₀ straight orbranched alkyl. The aryl includes a C₆ to C₆₀ monocyclic or polycyclicaryl. The heteroaryl includes a monocyclic or polycyclic heteroarylincluding S, O, or Se as a heteroatom. The arylamine includes an aminegroup substituted with one or two of the C₆ to C₆₀ monocyclic orpolycyclic aryl.

Examples of the compound of Formula 1 include a compound of thefollowing Formula 1-1 or 1-2.

In Formula 1-1,

Ar₁ to Ar₄ are the same as or different from each other, are eachindependently a substituted or unsubstituted C₆ to C₆₀ aryl, and maycombine with an adjacent group to form a monocyclic or polycyclicaromatic, aliphatic, or heterocyclic ring, and

Ar₅ is a substituted or unsubstituted C₆ to C₆₀ arylene.

According to an exemplary embodiment, in Formula 1-1, Ar₁ to Ar₄ are thesame as or different from each other, and are each independently phenyl,naphthyl, biphenyl, terphenyl, fluorenyl, or a group in which these aresubstituted with an alkyl such as methyl.

According to an exemplary embodiment, in Formula 1-1, A₅ is phenylene,naphthylene, biphenylene, terphenylene, fluorenylene, or a group inwhich these are substituted with an alkyl such as methyl, an aryl suchas phenyl, or an arylamine croup.

In Formula 1-2,

Ar₉ to Ar₁₄ are the same as or different from each other, are eachindependently a substituted or unsubstituted C₆ to C₆₀ aryl, and maycombine with an adjacent group to form a monocyclic or polycyclicaromatic, aliphatic, or heterocyclic ring, and Ar₆ to Ar₈ are the sameas or different from each other, and are each independently asubstituted or unsubstituted C₆ to C₆₀ arylene.

According to an exemplary embodiment, in Formula 1-2, Ar₉ to Ar₁₄ arethe same as or different from each other, and are each independentlyphenyl, naphthyl, biphenyl, terphenyl, fluorenyl, or a group in whichthese are substituted with an alkyl such as methyl.

According to an exemplary embodiment, in Formula 1-2, Ar₆ to Ar₈ are thesame as or different from each other, and are each independentlyphenylene, naphthylene, biphenylene, terphenylene, fluorenylene, or agroup in which these are substituted with an alkyl such as methyl, anaryl such as phenyl, or an arylamine group.

Specific examples of Formula 1 include the following formulas, but therange of exemplary embodiments described in the present specification isnot always limited thereto.

One specific example of the aryl amine compound includes NPB(N,N′-bis(naphthyl)-N,N′-bis(phenyl)benzidine).

An example of the polycyclic condensed ring compound includes a compoundof the following Formula 2.

In Formula 2, R^(1b) to R^(6b) may be each hydrogen, a halogen atom,nitrile (—CN), nitro (—NO₂), sulfonyl (—SO₂R), sulfoxide (—SOR),sulfonamide (—SO₂NR), sulfonate (—SO₃R), trifluoromethyl (—CF₃), ester(—COOR), amide (—CONHR or —CONRR′), a substituted or unsubstitutedstraight or branched C₁ to C₁₂ alkoxy, a substituted or unsubstitutedstraight or branched C₁ to C₁₂ alkyl, a substituted or unsubstitutedstraight or branched C₂ to C₁₂ alkenyl, a substituted or unsubstitutedaromatic or non-aromatic heterocyclic ring, a substituted orunsubstituted aryl, a substituted or unsubstituted mono- or di-arylamine, or a substituted or unsubstituted aralkyl amine, in which R andR′ are each a substituted or unsubstituted C₁ to C₆₀ alkyl, asubstituted or unsubstituted aryl, or a substituted or unsubstituted 5-to 7-membered heterocyclic ring.

Examples of Formula 2 include the following Formulas 2-1 to 2-6.

In the examples, the weight ratio of the content of the polycycliccondensed compound to the content of the aryl amine compound in thelight scattering layer may be in a range from 1/7 to 5/7. Within therange, appropriate roughness may be formed.

As another example, the light scattering layer may include a compound ofthe following Formula 3. The light scattering layer including a compoundof the following Formula 3 may be the first p-type organic materiallayer, or may be provided between the first p-type organic materiallayer and the n-type organic material layer. In particular, the compoundof the following Formula 3 may be used as a material of FIG. 3 whichsimultaneously exhibits the effect of the p-type organic material layerand the effect according to the light scattering layer. However, thescope of the present invention is not limited to the followingmaterials.

In Formula 3,

R_(1c) to R_(6c) may be the same as or different from each other, areeach independently a hydrogen atom; a C₁ to C₃₀ alkyl group which isunsubstituted or substituted with one or more groups selected from thegroup consisting of a halogen atom, an amino group, a nitrile group, anitro group, a C₁ to C₃₀ alkyl group, a C₂ to C₃₀ alkenyl group, a C₁ toC₃₀ alkoxy group, a C₃ to C₃₀ cycloalkyl group, a C₂ to C₃₀heterocycloalkyl group, a C₆ to C₃₀ aryl group, and a C₂ to C₃₀heteroaryl group; a C₃ to C₃₀ cycloalkyl group which is unsubstituted orsubstituted with one or more groups selected from the group consistingof a halogen atom, an amino group, a nitrile group, a nitro group, a C₁to C₃₀ alkyl group, a C₂ to C₃₀ alkenyl group, a C₁ to C₃₀ alkoxy group,a C₃ to C₃₀ cycloalkyl group, a C₃ to C₃₀ heterocycloalkyl group, a C₆to C₃₀ aryl group, and a C₂ to C₃₀ heteroaryl group; a C₆ to C₃₀ arylgroup which is unsubstituted or substituted with one or more groupsselected from the group consisting of a halogen atom, an amino group, anitrile group, a nitro group, a C₁ to C₃₀ alkyl group, a C₂ to C₃₀alkenyl group, a C₁ to C₃₀ alkoxy group, a C₃ to C₃₀ cycloalkyl group, aC₃ to C₃₀ heterocycloalkyl group, a C₆ to C₃₀ aryl group, and a C₂ toC₃₀ heteroaryl group; or a C₂ to C₃₀ heteroaryl group which isunsubstituted or substituted with one or more groups selected from thegroup consisting of a halogen atom, an amino group, a nitrile group, anitro group, a C₁ to C₃₀ alkyl group, a C₂ to C₃₀ alkenyl group, a C₁ toC₃₀ alkoxy group, a C₃ to C₃₀ cycloalkyl group, a C₃ to C₃₀heterocycloalkyl group, a C₆ to C₃₀ aryl group, and a C₂ to C₃₀heteroaryl group, and may form an aliphatic, aromatic, aliphatic hetero,or aromatic hetero condensation ring or a spiro bond in conjunction withan adjacent group, and n and m are each an integer from 0 to 4.

Examples of Formula 3 include the following Formula 3a.

R_(1c) to R_(4c) are the same as described above.

According to an exemplary embodiment, in Formula 3 or 3a, R_(1c) andR_(2c) may be a substituted or unsubstituted straight or branched C₁ toC₃₀ alkyl group or C₃ to C₃₀ cyclocalkyl group.

According to another exemplary embodiment, in Formula 3 or 3a, R_(1c)and R_(2c) may be methyl, ethyl, propyl, butyl, or cyclohexyl.

According to an exemplary embodiment, in Formula 3 or 3a, R_(3c) andR_(4c) may be a substituted or unsubstituted monocyclic or polycyclic C₆to C₃₀ aryl group.

According to another exemplary embodiment, in Formula 3 or 3a, R_(3c)and R_(4c) may be phenyl or naphthyl.

Examples of Formula 3 include compounds of the following Formulas 3-1 to3-5.

According to an exemplary embodiment, the light scattering layerincludes one organic material, which is a p-type organic material. Forexample, the compound of Formula 3 may be used as a p-type organicmaterial.

According to another exemplary embodiment, the light scattering layerincludes two organic materials, in which one of the organic materials isan n-type organic material, and the other one is a p-type organicmaterial. At this time, the n-type organic material may also serve as ap-type dopant for the p-type organic material. For example, the n-typeorganic material may be the compound of Formula 2, and the p-typeorganic material may be the compound of Formula 1.

FIGS. 1 to 3 illustrate a structure in which the light emitting layer isin direct contact with the anode. However, an organic material layer maybe additionally provided between the light emitting layer and the anode.The organic material layer which may be provided between the lightemitting layer and the anode may be a p-type organic material layer.Examples of the p-type organic material layer between the light emittinglayer and the anode include a hole injection layer, a hole transportinglayer, and the like.

In an exemplary embodiment according to FIG. 2 or FIG. 3, the firstp-type organic material layer is disposed as the organic material layerwhich is associated with the cathode, and the first n-type organicmaterial layer is disposed as the organic material layer providedbetween the first p-type organic material layer and the light emittinglayer. In the present specification, an “organic material layerassociated with the cathode” means an organic material layer which isdisposed closer to a cathode than an anode based on a light emittinglayer. At this time, the organic material layer associated with thecathode may include an organic material layer which is in physicalcontact with the cathode. However, in the exemplary embodiment, the casewhere an additional layer is provided between the organic material layerassociated with the cathode and the cathode is not completely ruled out.

In general, in an organic electroluminescent device, electrons areinjected and transported from a cathode to a light emitting layer, andholes are injected and transported from an anode to the light emittinglayer. Accordingly, in the organic electroluminescent device of therelated art, an n-type organic material layer, in which electrons areinjected or transported through the LUMO energy level, is disposedbetween the cathode and the light emitting layer.

It is opposite to the technology which has been thought in the field ofthe organic electroluminescent device that a p-type organic materiallayer is disposed as the organic material layer associated with thecathode. However, in the exemplary embodiment, the first p-type organicmaterial layer is disposed as the organic material layer associated withthe cathode. In addition, in the exemplary embodiment, the first n-typeorganic material layer is disposed between the first p-type organicmaterial layer and the light emitting layer. Here, an electric chargemay be generated between the first p-type organic material layer and thefirst n-type organic material layer. Among the electric chargesgenerated between the first p-type organic material layer and the firstn-type organic material layer, holes move toward the cathode through theHOMO energy level of the first p-type organic material layer. The holesmoving through the HOMO energy level of the first p-type organicmaterial layer escape in the direction of the cathode. Furthermore,among the electric charges generated between the first p-type organicmaterial layer and the first n-type organic material layer, electronmove toward the light emitting layer through the LUMO energy level ofthe first n-type organic material layer.

A method of injecting electric charges between the cathode and theorganic material layer associated with the cathode will be described inmore detail as follows.

The organic electroluminescent device of the related art includes then-type organic material layer as the organic material layer associatedwith the cathode. Accordingly, a barrier for injecting electrons fromthe cathode is a difference between the work function of the cathode andthe LUMO energy level of the n-type organic material layer. Accordingly,in the structure of the organic electroluminescent device in the relatedart, in order to reduce the electron injection barrier, an electroninjection layer such as an LiF layer is introduced, an electrontransporting layer is doped with an alkali metal or an alkaline earthmetal, or a metal having a low work function is used as a cathodematerial.

However, according to the exemplary embodiment, electric charges aregenerated between the first p-type organic material layer and the firstn-type organic material layer, and holes among the generated electriccharges move toward the cathode through the HOMO energy level of thefirst p-type organic material layer. FIG. 4 illustrates a schematic viewof the movement of the electric charge between the cathode and the firstp-type organic material layer in the organic electroluminescent deviceaccording to the exemplary embodiment, for example, the organicelectroluminescent device illustrated in FIG. 2 or 3. According to FIG.4, a hole transported to the HOMO energy level of the first p-typeorganic material layer meets an electron of the cathode and isannihilated. Accordingly, the electron injection barrier is not presentbetween the cathode and the first p-type organic material layer.Therefore, in the exemplary embodiment according to the presentspecification, it is not necessary to make an effort to reduce theelectron injection barrier from the cathode to the organic materiallayer.

Accordingly, in the exemplary embodiment of the present specification,it is possible to select a cathode material from materials havingvarious work functions. Further, it is not necessary to introduce anelectron injection layer or dope the organic material layer associatedwith the cathode with a metal material in order to reduce the electroninjection barrier.

Meanwhile, the light emitting characteristic in the organicelectroluminescent device is one of the important characteristics of thedevice. In order to efficiently emit light in the organicelectroluminescent device, it is important to achieve a charge balancein a light emitting region. For this purpose, electrons transported fromthe cathode and holes transported from the anode need to achieve aquantitative balance, and a point at which electrons and holes meet eachother to form exitons needs to be within the light emitting region.

Meanwhile, in the organic electroluminescent device, it is possible touse a method of controlling a cavity of the device according to a lightemitting color as one of the methods of increasing light emittingefficiency. The light emitting efficiency may be further increased bycontrolling the cavity of the device so as to be suitable for awavelength of a light emitting color. Here, the cavity of the devicemeans a length within which light may be resonated in the device. In anexample, when an upper electrode is a transparent electrode and a lowerelectrode is a reflective electrode, the cavity of the device may mean alength from a top of the upper electrode to a top of the lowerelectrode.

In addition, in the organic electroluminescent device, the distance fromthe light emitting layer to the cathode may also affect light loss by asurface plasmon, a metal, a waveguide mode, a substrate mode, anout-coupled mode, and the like. Accordingly, it may be necessary toadjust the distance from the light emitting layer to the cathode.

In order to control the distance from the cavity or light emitting layerof the device to the cathode thereof as described above, in thestructure of the organic electroluminescent device in the related art,when the thickness of the n-type organic material layer associated withthe cathode, for example, the electron transporting layer is increased,an imbalance of the electric charges may be caused. However, in theorganic electroluminescent device according to the exemplary embodimentof the present specification, it is possible to control the thickness ofthe first p-type organic material layer associated with the cathode.That is, controlling the thickness of the first p-type organic materiallayer may be used to control the distance between the cavity or lightemitting device of the device to the cathode thereof. In the exemplaryembodiment of the present specification, electrons reaching the lightemitting layer are not transported from the cathode, and are generatedbetween the first p-type organic material layer and the first n-typeorganic material layer. Accordingly, controlling the thickness of thefirst p-type organic material layer does not affect the charge balancein the light emitting layer. Furthermore, in the exemplary embodiment ofthe present invention, when the thickness of the first p-type organicmaterial layer is controlled, it is possible to minimize a problem inthat a driving voltage is increased according to the increase inthickness of the electron transporting layer which is an n-type organicmaterial layer in a structure of the related art.

In the structure of the related art, when a distance (D) from thecathode to the light emitting layer is controlled, the charge balance inthe light emitting layer may be affected. The reason is because theamount of electrons reaching the light emitting layer is varied when thethickness of the n-type organic material layer, for example, theelectron injection layer or the electron transporting layer iscontrolled. FIG. 5 illustrates a structure from the cathode to the lightemitting layer in the structure of the organic electroluminescent deviceas illustrated in FIG. 2 or 3. In the structure as described above, whena thickness Dh of the first p-type organic material layer associatedwith the cathode is controlled, controlling a distance D from a lightemitting point of the light emitting layer to the cathode, as a distancerelated to the cavity of the device, may be affected, but the chargebalance is not affected because a length De related to the amount ofelectrons is not affected. Here, the light emitting point in the lightemitting layer means a point at which light is actually emittedaccording to the balance of electrons and holes. The light emittingpoint may be varied depending on the material of the light emittinglayer. In the art to which the present invention pertains, a centralpoint of the light emitting layer or the interface between the lightemitting layer and another layer may be set as the light emitting point.

For example, when the cathode serves as a reflective plate, the distanceD from the light emitting point in the light emitting layer to thecathode may be controlled as an integer-fold of [refractive index of theorganic material layer*λ/4]. At this time, λ is a wavelength of lightemitted from the light emitting layer. Since lights having differentcolors have different wavelengths, it is possible to differently controlthe distance D from the light emitting point in the light emitting layerto the cathode depending on the color of light emitting from the lightemitting layer. Further, it is possible to differently control thedistance D from the light emitting point in the light emitting layer tothe cathode depending on the refractive index of the organic materiallayer. At this time, when the organic material layer is composed of twoor more layers, the refractive index of the organic material layer maybe calculated by obtaining the refractive index of each layer and thenobtaining the sum thereof.

In addition, when light proceeding toward the cathode reaches thesurface of the cathode and is reflected, the penetration depth of lightis varied depending on the type of cathode material. Accordingly, thetype of cathode material causes a change in phase of light reflectedfrom the surface of the cathode. At this time, in consideration of thephase difference to be changed, it is necessary to control the distanceD from the light emitting point in the light emitting layer to thecathode. Accordingly, a material of the cathode may also affect thedistance from the light emitting layer to the cathode.

When a phase matching of light proceeding from the light emitting layerto the cathode and light reflected from the cathode occurs, aconstructive interference occurs, and thus it is possible to implementbright light, and conversely, when a phase mismatching between thelights occurs, a destructive interference occurs, and thus a part of thelight is annihilated. According to the phenomenon of the phase matchingand the phase mismatching as described above, the brightness of theemitting light is shown in the form of a sine curve depending on thedistance from the light emitting layer to the cathode.

According to an exemplary embodiment of the present specification, inthe sine curve showing the brightness of the emitting light of thedevice according to the distance from the light emitting layer to thecathode, a value of an x-axis at a point where the brightness of lightis maximum may be set as the distance from the light emitting layer tothe cathode.

According to an exemplary embodiment of the present specification, adistance from a boundary between the first p-type organic material layerand the first n-type organic material layer or from a boundary betweenthe light scattering layer and the first n-type organic material layerto the light emitting layer and a distance from the anode to the lightemitting layer may be controlled such that an amount of holes in thelight emitting layer is balanced with that of electrons therein. Here,the balance between the amount of holes and the amount of electronsmeans that the holes and electrons injected into the light emittinglayer are recombined with each other in the light emitting layer andthus effectively form excitons for light emission, and the loss of holesand electrons involved in forming the excitons is minimized. Forexample, when the amount of holes in the device is larger than theamount of electrons therein, holes, which do not emit light and areannihilated, are generated in addition to holes involved in excitons dueto excessive holes, thereby causing a loss of the quantum efficiency inthe device. Conversely, when the amount of electrons is larger than theamount of holes, the loss of electrons may be caused. Accordingly, anattempt has been made to reduce the amounts of holes and electrons,which are annihilated without contributing to light emission, byachieving a quantitative balance of injected holes and electrons.

For example, as means for achieving a quantitative balance between holesand electrons in the light emitting layer, it is also important tocontrol a movement velocity of holes and electrons. When holes areexcessively present in the light emitting layer, a balance between holesand electrons may be achieved in the light emitting layer by increasingan injection velocity of electrons. In general, the hole mobility of amaterial provided between the anode and the light emitting layer, thatis, in a second electric charge transporting passage and transportingholes is faster than the electron mobility of a material providedbetween the cathode and the light emitting layer, that is, in a firstelectric charge transporting passage and transporting electrons. Forexample, the hole mobility of NPB is at the level of 8.8×10⁻⁴ cm²/Vs,whereas the electron mobility of Alq3 is at the level of 6.7×10⁻⁵cm²/Vs.

Accordingly, in enhancing the light emission efficiency of the device,it is important to enhance the electron mobility, and in increasing andusing the distance from the cathode to the light emitting layer, it maybe effective to increase the thickness of the first p-type organicmaterial layer rather than the thickness of the first n-type organicmaterial layer.

Therefore, according to an example, the distance from a boundary betweenthe first p-type organic material layer and the first n-type organicmaterial layer or from a boundary between the light scattering layer andthe first n-type organic material layer to the light emitting layer maybe configured to be shorter than the distance from the anode to thelight emitting layer. As a specific example, the distance from theboundary between the first p-type organic material layer and the firstn-type organic material layer or from the boundary between the lightscattering layer and the first n-type organic material layer to thelight emitting layer may be configured to be from 100 Å to 500 Å. Asanother specific example, the distance from the anode to the lightemitting layer may be configured to be from 500 Å to 5,000 Å. However,the specific value may be controlled differently according to thecharacteristics of the light emitting layer or the user.

According to an exemplary embodiment of the present specification, it ispossible to control the thickness of the first p-type organic materiallayer for stability of the device. When the thickness of the firstp-type organic material layer is controlled to be increased, thestability of the device may be further improved without affecting acharge balance in the device or an increase in voltage.

Here, the stability of the device means a degree which may prevent ashort phenomenon due to contact between the anode with the cathode,which may occur when the device is thin. In general, when the thicknessof the n-type organic material layer provided between the cathode andthe light emitting layer is controlled to be increased, stability of thedevice may be improved, but driving voltage thereof is rapidlyincreased, thereby reducing the power efficiency thereof. In order tosolve the problem in the related art, an attempt has been made tocontrol the thickness of the n-type organic material layer providedbetween the cathode and the light emitting layer to be increased anddope the organic material layer with a metal, but there is a problem inthat an increase in light absorption efficiency and a reduction inservice life occur, and the process thereof becomes complicated.

However, according to the description of the present specification, itis possible to increase the distance between the light emitting layerand the cathode by controlling the thickness of the first p-type organicmaterial layer, which does not affect the charge balance or the increasein voltage, instead of controlling the thickness of the n-type organicmaterial layer provided in the cathode and the light emitting layer.Accordingly, stability of the device is improved, and the increase indriving voltage is minimized, thereby increasing the power efficiency.

According to an example, in consideration of stability of the device,the distance from the cathode to the light emitting layer may beconfigured to be longer than the distance from the anode to the lightemitting layer. Even in such a configuration, the charge balance or theincrease in voltage is not affected unlike the related art. In aspecific example, the thickness of the first p-type organic materiallayer may be controlled to be 5 nm or more, and as the first p-typeorganic material layer becomes thick, the stability of the device may beenhanced. The upper limit of the thickness of the first p-type organicmaterial layer is not particularly limited, and may be determined bythose skilled in the art. For example, in consideration of ease ofprocess, the thickness of the first p-type organic material layer may beselected from 500 nm or less.

According to another exemplary embodiment of the present specification,the thickness of the first p-type organic material layer may becontrolled such that the cavity length of the organic electroluminescentdevice is an integer-fold of the wavelength of light emitted from thelight emitting layer. It is possible to improve light emissionefficiency caused by constructive interference of light by controllingthe cavity length of the organic electroluminescent device to be aninteger-fold of the wavelength of light as described above.

According to still another exemplary embodiment of the presentspecification, it is possible to control the distance from the boundarybetween the first p-type organic material layer and the first n-typeorganic material layer or from the boundary between the light scatteringlayer and the first n-type organic material layer to the light emittinglayer and the distance from the anode to the light emitting layer suchthat the amount of holes in the light emitting layer is balanced withthe amount of electrons therein, and to control the thickness of thefirst p-type organic material layer such that the cavity length of theorganic electroluminescent device is an integer-fold of the wavelengthof light emitted from the light emitting layer.

According to yet another exemplary embodiment of the presentspecification, it is possible to control a moving time of electrons fromthe boundary between the first p-type organic material layer and thefirst n-type organic material layer or from the boundary between thelight scattering layer and the first n-type organic material layer tothe light emitting layer and a moving time of holes from the anode tothe light emitting layer such that the holes and the electrons of thedevice are quantitatively balanced in the light emitting layer, and tocontrol the thickness of the first p-type organic material layer suchthat the cavity length of the organic electroluminescent device is aninteger-fold of the wavelength of light emitted from the light emittinglayer.

According to still yet another embodiment of the present specification,a difference between the HOMO energy level of the first p-type organicmaterial layer and the LUMO energy level of the first n-type organicmaterial layer is 2 eV or less. According to an exemplary embodiment ofthe present specification, the difference between the HOMO energy levelof the first p-type organic material layer and the LUMO energy level ofthe first n-type organic material layer may be more than 0 eV and 2 eVor less, or more than 0 eV and 0.5 eV or less. According to anotherexemplary embodiment of the present specification, a material for thefirst p-type organic material layer and the first n-type organicmaterial layer may be selected such that the difference between the HOMOenergy level of the first p-type organic material layer and the LUMOenergy level of the first n-type organic material layer is from 0.01 eVto 2 eV.

In the case where the energy difference between the HOMO energy level ofthe first p-type organic material layer and the LUMO energy level of thefirst n-type organic material layer is 2 eV or less, when the firstp-type organic material layer and the first n-type organic materiallayer are in contact with each other, an NP junction may be easilygenerated therebetween. In this case, a driving voltage for injectingelectrons may be reduced.

The first p-type organic material layer and the first n-type organicmaterial layer may be in contact with each other. In this case, an NPjunction is formed between the first p-type organic material layer andthe first n-type organic material layer. When the NP junction is formed,the difference between the HOMO energy level of the first p-type organicmaterial layer and the LUMO energy level of the first n-type organicmaterial layer is reduced. Accordingly, when an external voltage isapplied thereto, holes and electrons are easily formed from the NPjunction.

According to an exemplary embodiment of the present specification, thefirst p-type organic material layer is “non-doped”. When the firstp-type organic material layer is non-doped, unexpected absorption ofvisible light may be prevented by forming a charge transfer complexbetween the dopant and the host, thereby preventing light emissionefficiency from being reduced. When the first p-type organic materiallayer is non-doped, the first p-type organic material layer isdifferentiated from a layer having p-type semiconductor characteristicsby doping the organic material in the related art with a p-type dopant.The first p-type organic material layer does not exhibit p-typesemiconductor characteristics by the p-type dopant, but includes anorganic material having p-type semiconductor characteristics. In thecase of the organic material having p-type semiconductorcharacteristics, two or more organic materials may also be included inthe first p-type organic material layer.

According to an exemplary embodiment of the present specification, thework function of the cathode may have a value equal to or less than theHOMO energy level of the first p-type organic material layer.

When the work function of the cathode has a value equal to or less thanthe HOMO energy level of the first p-type organic material layer, aninjection barrier is not present when electrons are injected from thecathode to the HOMO energy level of the first p-type organic materiallayer.

According to an exemplary embodiment of the present specification, adifference between the HOMO energy level of the first p-type organicmaterial layer and the LUMO energy level of the first n-type organicmaterial layer may be 2 eV or less. According to another exemplaryembodiment of the present specification, the difference between the HOMOenergy level of the first p-type organic material layer and the LUMOenergy level of the first n-type organic material layer may be more than0 eV and 2 eV or less, or more than 0 eV and 0.5 eV or less. Accordingto still another exemplary embodiment of the present specification, amaterial for the first p-type organic material layer and the firstn-type organic material layer may be selected such that the differencebetween the HOMO energy level of the first p-type organic material layerand the LUMO energy level of the first n-type organic material layer isfrom 0.01 eV to 2 eV.

In the case where the energy difference between the HOMO energy level ofthe first p-type organic material layer and the LUMO energy level of thefirst n-type organic material layer is 2 eV or less, when the firstp-type organic material layer and the first n-type organic materiallayer are in contact with each other, an NP junction may be easilygenerated therebetween. In this case, a driving voltage for injectingelectrons may be reduced.

The cathode and the first p-type organic material layer may be incontact with each other. When the cathode and the first p-type organicmaterial layer are in contact with each other and the work function ofthe cathode is equal to or greater than the HOMO energy level of thefirst p-type organic material layer, electrons are easily injected fromthe cathode to the HOMO energy level of the first p-type organicmaterial layer even though the difference between the work function ofthe cathode and the HOMO energy level of the first p-type organicmaterial layer is large. This is because holes produced from the NPjunction between the first p-type organic material layer and the firstn-type organic material layer move along the first p-type organicmaterial layer toward the cathode. In general, when electrons move fromthe low energy level to the high energy level, there is no barrier.Further, when holes move from the high energy level to the low energylevel, no barrier is produced. Accordingly, electrons may move from thecathode to the HOMO energy level of the first p-type organic materiallayer without an energy barrier.

An additional layer may be additionally provided between the cathode andthe first p-type organic material layer. In this case, the HOMO energylevel of the additional layer may be equal to the work function of thecathode or the HOMO energy level of the first p-type organic materiallayer, or may be between the work function of the cathode or the HOMOenergy level of the first p-type organic material layer.

The first p-type organic material layer and the first n-type organicmaterial layer may be in contact with each other. In this case, an NPjunction is formed between the first p-type organic material layer andthe first n-type organic material layer. When the NP junction is formed,the difference between the HOMO energy level of the first p-type organicmaterial layer and the LUMO energy level of the first n-type organicmaterial layer is reduced. Accordingly, when an external voltage isapplied thereto, holes and electrons are easily formed from the NPjunction.

As a material for the first p-type organic material layer, it ispossible to use an organic material having p-type semiconductorcharacteristics. For example, an aryl amine compound may be used. As anexample of the aryl amine compound, there is a compound of the followingFormula 1.

The first n-type organic material layer is not limited to be composed ofa single material, and may be composed of one or two or more compoundshaving n-type semiconductor characteristics. In addition, the firstn-type organic material layer may be composed of a single layer, but mayalso include two or three or more layers. At this time, the two or morelayers may be composed of the same material, but may be composed ofdifferent materials. If necessary, at least one layer of the layersconstituting the first n-type organic material layer may be doped withan n-type dopant.

The first n-type organic material layer is not particularly limited aslong as the organic material layer is composed of a material which maymove electric charges through the LUMO energy level between the firstp-type organic material layer and the light emitting layer, as describedabove. For example, a compound of the following Formula 2 may be used.

Other examples, or synthesis methods and various characteristics ofFormula 2 are described in US Patent Application No. 2002-0158242, andU.S. Pat. Nos. 6,436,559 and 4,780,536, and the contents of thesedocuments are all incorporated in the present specification.

Furthermore, the first n-type organic material layer may include one ormore compounds selected from2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ),fluoro-substituted 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA),cyano-substituted 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA),naphthalene tetracaboxylic dianhydride (NTCDA), fluoro-substitutednaphthalene tetracaboxylic dianhydride (NTCDA), and cyano-substitutednaphthalene tetracaboxylic dianhydride (NTCDA).

Moreover, as a material for the first n-type organic material layer, itis possible to use an organic material having n-type semiconductorcharacteristics used as an electron injection or transporting material,which is known in the art. Specifically, the following material may beused, but the present invention is not limited thereto. For example, asan example of the material for the first n-type organic material layer,it is possible to use a compound having a functional group selected froman imidazole group, an oxazole group, a thiazole group, a quinolinegroup, and a phenanthroline group.

Specific examples of the compound having a functional group selectedfrom an imidazole group, an oxazole group, and a thiazole group includea compound of the following Formula 4 or 5.

In Formula 4, R¹ and R⁴ may be the same as or different from each other,are each independently a hydrogen atom; a C₁ to C₃₀ alkyl group which isunsubstituted or substituted with one or more groups selected from thegroup consisting of a halogen atom, an amino group, a nitrile group, anitro group, a C₁ to C₃₀ alkyl group, a C₂ to C₃₀ alkenyl group, a C₁ toC₃₀ alkoxy group, a C₃ to C₃₀ cycloalkyl group, a C₃ to C₃₀heterocycloalkyl group, a C₆ to C₃₀ aryl group, and a C₂ to C₃₀heteroaryl group; a C₃ to C₃₀ cycloalkyl group which is unsubstituted orsubstituted with one or more groups selected from the group consistingof a halogen atom, an amino group, a nitrile group, a nitro group, a C₁to C₃₀ alkyl group, a C₂ to C₃₀ alkenyl group, a C₁ to C₃₀ alkoxy group,a C₃ to C₃₀ cycloalkyl group, a C₃ to C₃₀ heterocycloalkyl group, a C₆to C₃₀ aryl group, and a C₂ to C₃₀ heteroaryl group; a C₅ to C₃₀ arylgroup which is unsubstituted or substituted with one or more groupsselected from the group consisting of a halogen atom, an amino group, anitrile group, a nitro group, a C₁ to C₃₀ alkyl group, a C₂ to C₃₀alkenyl group, a C₁ to C₃₀ alkoxy group, a C₃ to C₃₀ cycloalkyl group, aC₃ to C₃₀ heterocycloalkyl group, a C₆ to C₃₀ aryl group, and a C₂ toC₃₀ heteroaryl group; or a C₂ to C₃₀ heteroaryl group which isunsubstituted or substituted with one or more groups selected from thegroup consisting of a halogen atom, an amino group, a nitrile group, anitro group, a C₁ to C₃₀ alkyl group, a C₂ to C₃₀ alkenyl group, a C₁ toC₃₀ alkoxy group, a C₃ to C₃₀ cycloalkyl group, a C₃ to C₃₀heterocycloalkyl group, a C₆ to C₃₀ aryl group, and a C₂ to C₃₀heteroaryl group, and may form an aliphatic, aromatic, aliphatic hetero,or aromatic hetero condensation ring or a spiro bond in conjunction withan adjacent group; Ar¹ is a hydrogen atom, a substituted orunsubstituted aromatic ring, or a substituted or unsubstituted aromaticheterocyclic ring; X is O, S, or NR^(a); and R^(a) may be hydrogen, a C₁to C₇ aliphatic hydrocarbon, an aromatic ring, or an aromaticheterocyclic ring.

In Formula 5, X is O, S, NR^(b), or a C₁ to C₇ divalent hydrocarbongroup; A, D, and R^(b) are each hydrogen, a nitrile group (—CN), a nitrogroup (—NO₂), a C₁ to C₂₄ alkyl, a substituted aromatic ring including aC₅ to C₂₀ aromatic ring or a hetero atom, a halogen, or an alkylene oran alkylene including a hetero atom that may form a fused ring inconjunction with an adjacent ring; A and D may be connected to eachother to form an aromatic or hetero aromatic ring; B is a substituted orunsubstituted alkylene or arylene which conjugately or unconjugatelyconnects multiple heterocyclic rings as a linkage unit when n is 2 ormore, and a substituted or unsubstituted alkyl or aryl when n is 1; andn is an integer from 1 to 8.

Examples of the compound of Formula 4 include compounds known in KoreanPatent Application Laid-Open No. 2003-006773, and examples of thecompound of Formula 4 include compounds described in U.S. Pat. No.5,645,948 and compounds described in WO05/097756. All the contents ofthe documents are incorporated in the present specification.

Specifically, the compound of Formula 4 also includes the compound ofFormula 6.

In Formula 6, R⁵ to R⁷ are the same as or different from each other, andare each independently a hydrogen atom, a C₁ to C₂₀ aliphatichydrocarbon, an aromatic ring, an aromatic heterocyclic ring, or analiphatic or aromatic fused ring; Ar is a direct bond, an aromatic ringor an aromatic heterocyclic ring; X is O, S, or NR^(a); R^(a) is ahydrogen atom, a C₁ to C₇ aliphatic hydrocarbon, an aromatic ring, or anaromatic heterocyclic ring; and however, the case where R⁵ and R⁶ aresimultaneously hydrogen is ruled out.

Further, the compound of Formula 5 also includes the following compoundof Formula 7.

In Formula 7, Z is O, S, or NR^(b); R⁸ and R^(b) are a hydrogen atom, aC₁ to C₂₄ alkyl, a substituted aromatic ring including a C₅ to C₂₀aromatic ring or a hetero atom, a halogen, or an alkylene or an alkyleneincluding a hetero atom which may form a fused ring in conjunction witha benzazole ring; B is alkylene, arylene, a substituted alkylene, or asubstituted arylene which conjugately or unconjugately connects multiplebenzazoles as a linkage unit when n is 2 or more, and a substituted orunsubstituted alkyl or aryl when n is 1; and n is an integer from 1 to8.

For example, imidazole compounds having the following structures may beused:

Examples of the compound having a quinoline group include the followingcompounds of Formulas 8 to 14.

In Formulas 8 to 14,

n is an integer from 0 to 9, m is an integer of 2 or more,

R⁹ is selected from a ring structure with hydrogen, an alkyl group sucha methyl group and an ethyl group, a cycloalkyl group such as cyclohexyland norbornyl, an aralkyl group such as a benzyl group, an alkenyl groupsuch as a vinyl group and an allyl group, a cycloalkenyl group such acyclopentadienyl group and a cyclohexenyl group, an alkoxy group such asa methoxy group, an alkylthio group in which an oxygen atom with anether bond of an alkoxy group is substituted with a sulfur atom, an arylether group such as a phenoxy group, an aryl thioether group in which anoxygen atom with an ether bond of an aryl ether group is substitutedwith a sulfur atom, an aryl group such as a phenyl group, a naphthylgroup, and a biphenyl group, a heterocyclic group such as a furyl group,a thienyl group, an oxazolyl group, a pryridyl group, a quinolyl group,and a carbazolyl group, a halogen, a cyano group, an aldehyde group, acarbonyl group, a carboxyl group, an ester group, a carbamoyl group, anamino group, a nitro group, a silyl group such as a trimethylsilylgroup, a siloxanyl group which is a group having silicon through anether bond, and an adjacent substituent; and the substituents may beunsubstituted or substituted, and may be the same as or different fromeach other when n is 2 or more; and

Y is a divalent group of groups of R⁹.

The compounds of Formulas 8 to 14 are described in Korean PatentApplication Laid-Open No. 2007-0118711, and the contents of thedocuments are all incorporated in the present specification byreference.

Examples of the compound having a phenanthroline group include thefollowing compounds of Formulas 15 to 25, but are not limited thereto.

In Formulas 15 to 18,

m is an integer of 1 or more, n and p are an integer, n+p is 8 or less,

when m is 1, R¹⁰ and R¹¹ are selected from a ring structure withhydrogen, an alkyl group such a methyl group and an ethyl group, acycloalkyl group such as cyclohexyl and norbornyl, an aralkyl group suchas a benzyl group, an alkenyl group such as a vinyl group and an allylgroup, a cycloalkenyl group such a cyclopentadienyl group and acyclohexenyl group, an alkoxy group such as a methoxy group, analkylthio group in which an oxygen atom with an ether bond of an alkoxygroup is substituted with a sulfur atom, an aryl ether group such as aphenoxy group, an aryl thioether group in which an oxygen atom with anether bond of an aryl ether group is substituted with a sulfur atom, anaryl group such as a phenyl group, a naphthyl group, and a biphenylgroup, a heterocyclic group such as a furyl group, a thienyl group, anoxazolyl group, a pryridyl group, a quinolyl group, and a carbazolylgroup, a halogen, a cyano group, an aldehyde group, a carbonyl group, acarboxyl group, an ester group, a carbamoyl group, an amino group, anitro group, a silyl group such as a trimethylsilyl group, a siloxanylgroup which is a group having silicon through an ether bond, and anadjacent substituent;

when m is 2 or more, R¹⁰ is a direct bond or a divalent or more group ofthe above-described groups, and R¹¹ is the same as the case where m is1, and

the substituents may be unsubstituted or substituted, and when n or p is2 or more, the substituents may be the same as or different from eachother.

The compounds of Formulas 15 to 18 are described in Korean PatentApplication Laid-Open Nos. 2007-0052764 and 2007-0118711, and thecontents of the documents are all incorporated in the presentspecification by reference.

In Formulas 19 to 22, R^(1a) to R^(8a) and R^(1b) to R^(10b) are each ahydrogen atom, a substituted or unsubstituted aryl group having from 5to 60 nucleus atoms, a substituted or unsubstituted pyridyl group, asubstituted or unsubstituted quinolyl group, a substituted orunsubstituted alkyl group having from 1 to 50 carbon atoms, asubstituted or unsubstituted cycloalkyl group having from 3 to 50 carbonatoms, a substituted or unsubstituted aralkyl group having from 6 to 50nucleus atoms, a substituted or unsubstituted alkoxy group having from 1to 50 carbon atoms, a substituted or unsubstituted aryloxy group havingfrom 5 to 50 nucleus atoms, a substituted or unsubstituted arylthiogroup having from 5 to 50 nucleus atoms, a substituted or unsubstitutedalkoxycarbonyl group having from 1 to 50 carbon atoms, an amino groupsubstituted with a substituted or unsubstituted aryl group having from 5to 50 nucleus atoms, a halogen atom, a cyano group, a nitro group, ahydroxyl group, or a carboxyl group, and may be bonded to each other tofrom an aromatic ring, and L is a substituted or unsubstituted arylenegroup having from 6 to 60 carbon atoms, a substituted or unsubstitutedpyridinylene group, a substituted or unsubstituted quinolynylene group,or a substituted or unsubstituted fluorenylene group. The compounds ofFormulas 19 to 22 are described in Japanese Patent Application Laid-OpenNo. 2007-39405, and the content of the document is all incorporated inthe present specification by reference.

In Formulas 23 and 24, d¹, d³ to d¹⁰, and g¹ are each hydrogen, or anaromatic or aliphatic hydrocarbon group, m and n are an integer from 0to 2, and p is an integer from 0 to 3. The compounds of Formulas 23 and24 are described in US Patent Publication No. 2007/0122656, and thecontent of the document is all incorporated in the present specificationby reference.

In Formula 25, R^(1c) to R^(6c) are each a hydrogen atom, a substitutedor unsubstituted alkyl group, a substituted or unsubstituted aralkylgroup, a substituted or unsubstituted aryl group, a substituted orunsubstituted heterocyclic group, or a halogen atom, and Ar^(1c) areAr^(2c) are each selected from the following structural formulas.

In the structural formulas, R₁₇ to R₂₃ are each a hydrogen atom, asubstituted or unsubstituted alkyl group, a substituted or unsubstitutedaralkyl group, a substituted or unsubstituted aryl group, a substitutedor unsubstituted heterocyclic group, or a halogen atom. The compound ofFormula 25 is described in Japanese Patent Application Laid-Open No.2004-107263, and the content of the document is all incorporated in thepresent specification by reference.

At least one organic material layer may be further included between thefirst n-type organic material layer and the light emitting layer. Anelectron transporting layer, a hole blocking layer, and the like havingone or two or more layers may be provided between the first n-typeorganic material layer and the light emitting layer.

Hereinafter, each layer constituting the organic electroluminescentdevice according to the exemplary embodiment of the presentspecification will be described in detail. Materials of each layer to bedescribed below may be a single material or a mixture of two or morematerials.

Anode

An anode includes a metal, a metal oxide, or a conductive polymer. Theconductive polymer may include an electrically conductive polymer. Forexample, the anode may have a work function value from about 3.5 eV toabout 5.5 eV. Examples of exemplary conductive materials include carbon,aluminum, vanadium, chromium, copper, zinc, silver, gold, other metals,and an alloy thereof; zinc oxide, indium oxide, tin oxide, indium tinoxide (ITO), indium zinc oxide, and other similar metal oxides; amixture of oxide and metal such as ZnO:Al and SnO₂:Sb, and the like. Asa material for the anode, a transparent material or an opaque materialmay be used. In the case of a structure in which light is emitted in theanode direction, the anode may be transparently formed. Here,transparency is sufficient as long as light emitted from an organicmaterial layer may be transmitted, and the transmittance of light is notparticularly limited.

For example, when the organic electroluminescent device according to thepresent specification is a top emission type, and the anode is formed onthe substrate before the organic material layer and the cathode areformed, an opaque material having excellent optical reflectance may alsobe used as a material for the anode in addition to a transparentmaterial. For example, when the organic electroluminescent deviceaccording to the present specification is a bottom emission type, andthe anode is formed on the substrate before the organic material layerand the cathode are formed, as a material for the anode, a transparentmaterial is used, or an opaque material needs to be formed as a thinfilm enough to be transparent.

In the organic electroluminescent device according to the description ofthe present specification, a second p-type organic material layer may beincluded between the light emitting layer and the anode between whichthe second electric charge transporting passage is formed. FIG. 8illustrates an energy flow when the second p-type organic material layeris provided. The second p-type organic material layer may be a holeinjection layer (HIL) or a hole transporting layer (HTL). As a materialfor the second p-type organic material layer, it is possible to use theabove-described materials mentioned as a material for the first p-typeorganic material layer.

A fourth n-type organic material layer may be provided between thesecond p-type organic material layer and the anode. Here, the differencebetween the HOMO energy level of the second p-type organic materiallayer and the LUMO energy level of the fourth n-type organic materiallayer may be 2 eV or less, or 1 eV or less, for example, about 0.5 eV.The second p-type organic material layer and the fourth n-type organicmaterial layer may be in contact with each other. Accordingly, thesecond p-type organic material layer and the fourth n-type organicmaterial layer may form an NP junction. FIG. 9 illustrates an energyflow when the fourth n-type organic material layer is provided.

The difference between the LUMO energy level of the fourth n-typeorganic material layer and the work function of the anode may be 4 eV orless. The fourth n-type organic material layer and the anode may be incontact with each other.

The fourth n-type organic material layer may have a LUMO energy levelfrom about 4 eV to about 7 eV, and an electron mobility from about 10⁻⁸cm²/Vs to 1 cm²/Vs, or from about 10⁻⁶ cm²/Vs to about 10⁻² cm²/Vs. Thefourth n-type organic material layer having an electric mobility withinthe range is advantageous for efficient injection of holes.

The fourth n-type organic material layer may also be formed of amaterial which may be vacuum deposited, or a material which may bethin-film molded by a solution process. Specific examples of the fourthn-type organic material include2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ),fluoro-substituted 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA),cyano-substituted PTCDA, naphthalene tetracaboxylic dianhydride (NTCDA),fluoro-substituted NTCDA, cyano-substituted NTCDA, or hexanitrilehexaazatriphenylene (HAT), but are not limited thereto.

When the fourth n-type organic material layer and the second p-typeorganic material layer form an NP junction, holes formed from the NPjunction are transported to the light emitting layer through the secondp-type organic material layer.

The second p-type organic material layer may include an aryl aminecompound, a conductive polymer, or a block copolymer having both aconjugated portion and an unconjugated portion, and the like, but is notlimited thereto.

Light Emitting Layer (EML)

In the light emitting layer, hole transfer and electron transfer occurat the same time, and thus the light emitting layer may have both n-typecharacteristics and p-type characteristics. For convenience, whenelectron transport is faster than hole transport, the light emittinglayer may be defined as an n-type light emitting layer, and when holetransport is faster than electron transport, the light emitting layermay be defined as a p-type light emitting layer.

The n-type light emitting layer includes aluminum tris(8-hydroxyquinoline) (Alq₃); 8-hydroxy quinoline beryllium (BAlq); abenzoxazole-based compound, a benzthiazole-based compound orbenzimidazole-based compound; a polyfluorene-based compound; a silacyclopentadiene (silole)-based compound, and the like, but is notlimited thereto.

The p-type light emitting layer includes a carbazole-based compound; ananthracene-based compound; a polyphenylenevinylene (PPV)-based polymer;or a spiro compound, and the like, but is not limited thereto.

Electron Transporting Layer (ETL)

In the present specification, the first n-type organic material layermay also be formed as an electron transporting layer, and an additionalsecond n-type organic material layer may also be provided between thefirst n-type organic material layer and the light emitting layer. FIG. 6illustrates an energy flow when the second n-type organic material layeris provided. The second n-type organic material layer may also serve asan electron transporting layer or a hole blocking layer. It is preferredthat a material for the second n-type organic material layer is amaterial having a large electron mobility so as to transport electronswell. A third n-type organic material layer may also be provided betweenthe second n-type organic material layer and the light emitting layer.The third n-type organic material layer may also serve as an electrontransporting layer or a hole blocking layer. FIG. 7 illustrates anenergy flow when the third n-type organic material layer is provided.

It is preferred that the first n-type organic material layer is composedof a material having a LUMO energy level of 2 eV or less and the firstp-type organic material layer is composed of a material having a HOMOenergy level of 2 eV or less, as described above. According to anexample, the first n-type organic material layer may have a LUMO energylevel from 5 eV to 7 eV.

It is preferred that the second n-type organic material layer has a LUMOenergy level smaller than the LUMO energy level of the first n-typeorganic material layer. According to an example, the second n-typeorganic material layer may have a LUMO energy level from 2 eV to 3 eV.According to an example, the second n-type organic material layer mayhave a HOMO energy level from 5 eV to 6 eV, specifically, from 5.8 eV to6 eV.

The second or third n-type organic material layer includes aluminumtris(8-hydroxy quinoline) (Alq₃); an organic compound including an Alq₃structure; a hydroxyflavone-metal complex or a sila cyclopentadiene(silole)-based compound, and the like, but is not limited thereto. As amaterial for the second or third n-type organic material layer, theaforementioned material for the first n-type organic material layer mayalso be used. The second or third n-type organic material layer may bedoped with an n-type dopant. According to an exemplary embodiment, whenany one of the second n-type organic material layer and the third n-typeorganic material layer is doped with the n-type dopant, a host materialof the doped layer and a material of the undoped layer may be the sameas each other.

The n-type dopant may be an organic material or an inorganic material.When the n-type dopant is an inorganic material, the n-type dopant mayinclude an alkali metal, for example, Li, Na, K, Rb, Cs, or Fr; analkaline earth metal, for example, Be, Mg, Ca, Sr, Ba, or Ra; a rareearth metal, for example, La, Ce, Pr, Nd, Sm, Eu, Tb, Th, Dy, Ho, Er,Em, Gd, Yb, Lu, Y, or Mn; or a metal compound including one or moremetals of the metals. Alternatively, the n-type dopant may also be amaterial including cyclopentadiene, cycloheptatriene, a six-memberedheterocyclic ring, or a condensed ring including these rings. At thistime, the doping concentration may be from 0.01% by weight to 50% byweight, or from 1% by weight to 10% by weight.

As a specific example, the organic electroluminescent device includesfirst to third n-type organic material layers, in which the first n-typeorganic material layer may include the compound of Formula 1, and thesecond n-type organic material layer may be doped with an n-type dopant.At this time, the second n-type organic material layer and the thirdn-type organic material layer may include the compound of Formula 5 as ahost material.

Cathode

As described above, in the present specification, a cathode material maybe selected from materials having various work functions by includingthe above-described first p-type organic material layer and first n-typeorganic material layer. It is preferred that the cathode material isusually a material having a small work function so as to facilitateelectron injection. However, in the present specification, a materialhaving a large work function may also be applied. Specifically, in thepresent specification, it is possible to use, as the cathode material, amaterial having a work function which is equal to or larger than theHOMO energy level of the first p-type organic material layer. Forexample, in the present specification, a material having a work functionfrom 2 eV to 5 eV may be used as the cathode material. The cathodeincludes a metal such as magnesium, calcium, sodium, potassium,titanium, indium, yttrium, lithium, gadolinium, aluminum, silver, tin,and lead, or an alloy thereof; a multi-layer structured material such asLiF/Al or LiO₂/Al, and the like.

When Al is used as the cathode material, it is possible to provide adevice capable of being efficiently operated by using Al either alone ortogether with LiF or Liq. In particular, when Ag is used as the cathodematerial, a device according to the related art is not operated wellwhen Ag is used either alone or together with LiF or Liq, and thus as anorganic material layer associated with the cathode, a layer composed ofa metal such as an alkali metal or an alkaline earth metal, or anorganic material layer doped with a metal needs to be used. However, inthe exemplary embodiments described in the present specification, amaterial having a large work function, such as Ag, may be used as thecathode material without a metal layer or an organic material layerdoped with a metal, as described above. In addition, in the exemplaryembodiments described in the present specification, a transparentconductive oxide having a high work function such as IZO (work functionfrom 4.8 eV to 5.2 eV) may also be used as the cathode material.

According to an exemplary embodiment of the present specification, thecathode may be provided so as to be in physical contact with the organicmaterial layer. The organic material layer in contact with the cathodemay be the above-described first p-type organic material layer, and maybe an additional organic material layer. Here, the organic materiallayer which is in contact with the cathode may be non-doped.

In the organic electroluminescent device in the related art, when acathode of a material having a large work function, such as Al or Ag, isused, it is necessary to dope an inorganic material layer such as an LiFlayer between an organic material layer and the cathode, or the organicmaterial layer with a metal. In the related art, when the cathode is incontact with the organic material layer without using the inorganicmaterial layer or the organic material layer doped with the metal asdescribed above, only a material having a work function of 2 eV or moreand less than 3.5 eV may be used as the cathode material. However, inthe organic electroluminescent device according to the presentspecification, even when the cathode is in contact with the organicmaterial layer, a cathode may be configured by using a material having awork function of 3.5 eV or more by the first p-type organic materiallayer and the first n-type organic material layer.

According to an exemplary embodiment of the present specification, thecathode is provided so as to be in physical contact with the organicmaterial layer, and the cathode is composed of a material having a workfunction of 3.5 eV or more.

According to an exemplary embodiment of the present specification, thecathode is provided so as to be in physical contact with the organicmaterial layer, and the cathode is composed of a material having a workfunction of 4 eV or more.

According to an exemplary embodiment of the present specification, thecathode is provided so as to be in physical contact with the organicmaterial layer, and the cathode is composed of a material having a workfunction of 4.5 eV or more.

The upper limit of the work function of the material constituting thecathode is not particularly limited, but it is possible to use amaterial having a work function of 5.5 eV or less from the viewpoint ofselecting a material.

The cathode may be formed of a material which is the same as the anode.In this case, the cathode may be formed of the aforementioned materialsexemplified as the material of the anode. Alternatively, the cathode orthe anode may include a transparent material.

The thickness or shape or pattern form of the organic material layerdescribed in the present specification, for example, the first andsecond p-type organic material layer, the first to fourth n-type organicmaterial layer, the cathode, and the anode may be selected by thoseskilled in the art depending on the type of material or the rolerequired in the device. The organic electroluminescent device accordingto an exemplary embodiment of the present specification may be a deviceincluding a light extraction structure.

In an exemplary embodiment of the present specification, the organicelectroluminescent device further includes a substrate provided on asurface facing a surface on which the organic material layer of theanode or the cathode is provided, and a light extraction layer providedbetween the substrate and the anode or the cathode, or on a surfacefacing a surface on which the anode or the cathode of the substrate isprovided.

In other words, the organic electroluminescent device may furtherincludes an internal light extraction layer between the substrate, whichis provided on a surface facing a surface on which the organic materiallayer of the anode or the cathode is provided, and the anode or thecathode. In another exemplary embodiment, an external light extractionlayer may be additionally provided on a surface opposite to a surface onwhich the anode or the cathode is provided on the substrate.

In the present specification, the internal light extraction layer or theexternal light extraction layer is not particularly limited as long asthe layer has a structure which may induce light scattering so as toimprove the light extraction efficiency of the device. In an exemplaryembodiment, the light extraction layer may be formed by using a filmhaving a structure in which scattering particles are dispersed in abinder, or unevenness.

In addition, the light extraction layer may be directly formed on asubstrate by a method such as spin coating, bar coating, slit coating,and the like, or may be formed by a method of manufacturing the layer ina film form and attaching the layer.

In an exemplary embodiment of the present specification, the organicelectroluminescent device is a flexible organic electroluminescentdevice. In this case, the substrate includes a flexible material. Forexample, it is possible to use glass having a flexible thin film form,plastic, or a substrate having a film form.

A material of the plastic substrate is not particularly limited, butgenerally, a film of PET, PEN, PI, and the like may be used in the formof a single layer or plural layers.

In an exemplary embodiment of the present specification, a displayapparatus including the organic electroluminescent device is provided.

In an exemplary embodiment of the present specification, an illuminationapparatus including the organic electroluminescent device is provided.

Hereinafter, specific experimental examples of the above-describedexemplary embodiments will be described. However, the followingexperimental examples are illustrative only, and are not intended tolimit the range of the exemplary embodiments.

Experimental Example 1

An anode having a thickness of 1,000 Å was formed on a substrate by asputtering method using IZO, and a p-type hole injection layer having athickness of 500 Å was formed thereon by thermally vacuum depositing anm-MTDATA of the following Formula. Subsequently, a p-type holetransporting layer having a thickness of 400 Å was formed thereon byvacuum depositing the NPB of the following Formula.

Subsequently, a light emitting layer having a thickness of 300 Å wasformed by doping a CBP of the following Formula with an Ir(ppy)₃ of thefollowing Formula in an amount of 10% by weight. A hole blocking layerhaving a thickness of 50 Å was formed thereon using a BCP of thefollowing formula.

An organic material layer having a thickness of 100 Å was formed thereonusing an electron transporting material of the following formula, and anelectron transporting layer having a thickness of 50 Å was formedthereon by doping the electron transporting material of the followingformula with Ca in an amount of 10% by weight.

A first n-type organic material layer having a thickness of 300 Å wasformed thereon using an HAT of the following Formula, which is an n-typeorganic material. A light scattering layer was formed thereon using amaterial selected from A to F described in the following Table 1.Subsequently, a first p-type organic material layer having a thicknessof 50 Å was formed using the NPB as a p-type organic material.

TABLE 1 Thickness of organic material Material layer (Å) A Compound ofFormula 2-1 1,000 B NPB 1,000 C Compound of Formula 2-1:NPB = 1:1 weightratio 2,000 D Compound of Formula 2-1:NPB = 7:3 weight ratio 1,000 ECompound of Formula 2-1:NPB = 3:7 weight ratio 1,000 F Compound ofFormula 2-1:NPB = 1:1 weight ratio 1,000

Finally, an organic electroluminescent device was manufactured byforming Ag as the cathode to have a thickness of 2,000 Å.

The deposition rate of the organic material in the process wasmaintained at a level from 0.5 Å/sec to 1 Å/sec, and the degree ofvacuum during the deposition was maintained at a level from 2×10⁻⁷ torrto 2×10⁻⁸ torr.

FIGS. 10A to 10F illustrate SEM photographs illustrating the surface ofthe organic material layers formed by using the materials described inthe Table. In FIGS. 10A, 10C, 10E, and 10F, roughness was observed to belarge. In particular, in FIG. 10E, the roughness of particles formed bymaterials forming the layer was observed most frequently, and in thiscase, an effect was exhibited that the light extraction efficiency wasincreased by about 20% compared to the device B according to the changein passage of light generated in the device.

TABLE 2 Driving voltage External quantum (@ 5 mA/cm²) efficiency (@ 5mA/cm²) F1G. 10A 6.5 V 9.0% F1G. 10B 7.8 V 9.3% F1G. 10C 8.2 V 11.6%F1G. 10D 8.0 V 9.5% F1G. 10E 9.5 V 11.2% F1G. 10F 8.0 V 9.7%

Experimental Example 2

An anode having a thickness of 1,000 Å was formed on a substrate by asputtering method using IZO, and a p-type hole injection layer having athickness of 500 Å was formed thereon by thermally vacuum depositing them-MTDATA of the above Formula. Subsequently, a p-type hole transportinglayer having a thickness of 400 Å was formed thereon by vacuumdepositing the NPB of the above Formula.

Subsequently, a light emitting layer having a thickness of 300 Å wasformed by doping the CBP of the above Formula with an Ir(ppy)₃ of thefollowing Formula in an amount of 10% by weight. A hole blocking layerhaving a thickness of 50 Å was formed thereon using the BCP of the aboveFormula.

An organic material layer having a thickness of 100 Å was formed thereonusing the electron transporting material of the above Formula, and anelectron transporting layer having a thickness of 50 Å was formedthereon by doping the electron transporting material of the aboveformula with Ca in an amount of 10% by weight.

A first n-type organic material layer having a thickness of 300 Å wasformed thereon using the HAT of the above Formula, which is an n-typeorganic material. A compound of the following Formula 3-1, which is alayer capable of serving as the first p-type organic material layer andthe scattering layer, was formed to have a thickness of 500 Å and 5,000Å, respectively, and was compared with the devices formed to have athickness of 500 Å and 5,000 Å respectively by using the NPB as theComparative Examples in terms of characteristics thereof.

Finally, an organic electroluminescent device was manufactured byforming Ag as the cathode to have a thickness of 2,000 Å.

Characteristics of the device manufactured are shown in the followingTable 3.

TABLE 3 Driving voltage External quantum (@ 5 mA/cm²) efficiency (@ 5mA/cm²) Formula 3-1 500 Å 8.6 V 6.1% Formula 3-1 5,000 Å 9.6 V 7.5% NPB500 Å 7.4 V 5.0% NPB 5,000 Å 9.0 V 6.3%

Table 3 shows a result that similarly to Experimental Example 1, thelight extraction efficiency of a device in which a scattering layer isdisposed at the cathode interface was increased by about 20% compared toa device in which the scattering layer is not disposed at the cathodeinterface.

In order to explore the possibility of using each layer as the lightscattering layer, surface characteristics of a glass substrate, surfacecharacteristics of the ITO layer after being formed on the glasssubstrate, and surface characteristics of the compound layer of Formula3-1 after being formed on the ITO layer on the glass substrate werecaptured as SEM photographs for each thickness of each layer, and theresults are illustrated in FIGS. 11A to 11C. It can be seen that thecompound of Formula 3-1 may be used as a material of the lightscattering layer described in the present specification, depending onthe thickness of the layer. In FIG. 11A to 11C, the thickness means athickness of the uppermost layer.

1. An organic electroluminescent device comprising: an anode; a cathode;a light emitting layer provided between the anode and the cathode; and alight scattering layer provided between the light emitting layer and thecathode.
 2. The organic electroluminescent device of claim 1, furthercomprising: a first electric charge transporting passage providedbetween the light emitting layer and the cathode; and a second electriccharge transporting passage provided between the light emitting layerand the anode, wherein the first electric charge transporting passagecomprises a first p-type organic material layer associated with thecathode; and a first n-type organic material layer provided between thefirst p-type organic material layer and the light emitting layer, andthe light scattering layer is the first p-type organic material layer,or is provided between the first p-type organic material layer and thefirst n-type organic material layer.
 3. The organic electroluminescentdevice of claim 1, further comprising: a buffer layer provided betweenthe light emitting layer and the cathode, wherein the buffer layerincludes: a first p-type organic material layer associated with thecathode; and a first n-type organic material layer provided between thefirst p-type organic material layer and the light emitting layer, andthe light scattering layer is the first p-type organic material layer,or is provided between the first p-type organic material layer and thefirst n-type organic material layer.
 4. The organic electroluminescentdevice of claim 1, further comprising: a first p-type organic materiallayer provided between the light emitting layer and the cathode; and afirst n-type organic material layer provided between the light emittinglayer and the first p-type organic material layer, wherein the lightscattering layer is the first p-type organic material layer, or isprovided between the first p-type organic material layer and the firstn-type organic material layer.
 5. The organic electroluminescent deviceof claim 1, wherein the light scattering layer comprises a lightscattering structure provided in or on a surface of the layer.
 6. Theorganic electroluminescent device of claim 5, wherein the lightscattering layer is formed of an organic material.
 7. The organicelectroluminescent device of claim 5, wherein the light scatteringstructure is a particle structure formed by constituting a cluster oforganic material molecules.
 8. The organic electroluminescent device ofclaim 5, wherein the light scattering structure is formed by depositingan organic material.
 9. The organic electroluminescent device of claim7, wherein a particle diameter of the particle is from 0.5 micron to 30micron.
 10. The organic electroluminescent device of claim 7, wherein adegree of roughness of the particle structure is from 2 nm to 50 nm. 11.The organic electroluminescent device of claim 5, wherein the lightscattering layer comprises a polycyclic condensed ring compound and anaryl amine compound.
 12. The organic electroluminescent device of claim11, wherein the aryl amine compound comprises a compound of thefollowing Formula 1:

in Formula 1, Ar₁, Ar₂, and Ar₃ are each independently hydrogen or ahydrocarbon group.
 13. The organic electroluminescent device of claim12, wherein the aryl amine compound comprises NPB(N,N′-bis(naphthyl)-N,N′-bis(phenyl)benzidine).
 14. The organicelectroluminescent device of claim 11, wherein the polycyclic condensedring compound comprises a compound of the following Formula 2:

in Formula 2, R^(1b) to R^(6b) are each hydrogen, a halogen atom,nitrile (—CN), nitro (—NO₂), sulfonyl (—SO₂R), sulfoxide (—SOR),sulfonamide (—SO₂NR), sulfonate (—SO₃R), trifluoromethyl (—CF₃), ester(—COOR), amide (—CONHR or —CONRR′), a substituted or unsubstitutedstraight or branched C₁ to C₁₂ alkoxy, a substituted or unsubstitutedstraight or branched C₁ to C₁₂ alkyl, a substituted or unsubstitutedstraight or branched C₂ to C₁₂ alkenyl, a substituted or unsubstitutedaromatic or non-aromatic heterocyclic ring, a substituted orunsubstituted aryl, a substituted or unsubstituted mono- or di-arylamine, or a substituted or unsubstituted aralkyl amine, wherein R and R′are each a substituted or unsubstituted C₁ to C₆₀ alkyl, a substitutedor unsubstituted aryl, or a substituted or unsubstituted 5- to7-membered heterocyclic ring.
 15. The organic electroluminescent deviceof claim 14, wherein the Formula 2 is selected from the followingFormulas 2-1 to 2-6:


16. The organic electroluminescent device of claim 11, wherein a weightratio of a content of the polycyclic condensed compound to a content ofthe aryl amine compound in the light scattering layer is from 1/7 to5/7.
 17. The organic electroluminescent device of claim 5, wherein thelight scattering layer comprises a compound of the following Formula 3:

in Formula 3, R_(1c) to R_(6c) are the same as or different from eachother, are each independently a hydrogen atom; a C₁ to C₃₀ alkyl groupwhich is unsubstituted or substituted with one or more groups selectedfrom the group consisting of a halogen atom, an amino group, a nitrilegroup, a nitro group, a C₁ to C₃₀ alkyl group, a C₂ to C₃₀ alkenylgroup, a C₁ to C₃₀ alkoxy group, a C₃ to C₃₀ cycloalkyl group, a C₃ toC₃₀ heterocycloalkyl group, a C₆ to C₃₀ aryl group, and a C₂ to C₃₀heteroaryl group; a C₃ to C₃₀ cycloalkyl group which is unsubstituted orsubstituted with one or more groups selected from the group consistingof a halogen atom, an amino group, a nitrile group, a nitro group, a C₁to C₃₀ alkyl group, a C₂ to C₃₀ alkenyl group, a C₁ to C₃₀ alkoxy group,a C₃ to C₃₀ cycloalkyl group, a C₃ to C₃₀ heterocycloalkyl group, a C₆to C₃₀ aryl group, and a C₂ to C₃₀ heteroaryl group; a C₆ to C₃₀ arylgroup which is unsubstituted or substituted with one or more groupsselected from the group consisting of a halogen atom, an amino group, anitrile group, a nitro group, a C₁ to C₃₀ alkyl group, a C₂ to C₃₀alkenyl group, a C₁ to C₃₀ alkoxy group, a C₃ to C₃₀ cycloalkyl group, aC₃ to C₃₀ heterocycloalkyl group, a C₆ to C₃₀ aryl group, and a C₂ toC₃₀ heteroaryl group; or a C₂ to C₃₀ heteroaryl group which isunsubstituted or substituted with one or more groups selected from thegroup consisting of a halogen atom, an amino group, a nitrile group, anitro group, a C₁ to C₃₀ alkyl group, a C₂ to C₃₀ alkenyl group, a C₁ toC₃₀ alkoxy group, a C₃ to C₃₀ cycloalkyl group, a C₃ to C₃₀heterocycloalkyl group, a C₆ to C₃₀ aryl group, and a C₂ to C₃₀heteroaryl group, and are able to form an aliphatic, aromatic, aliphatichetero, or aromatic hetero condensation ring or a spiro bond inconjunction with an adjacent group, and n and m are each an integer from0 to
 4. 18. The organic electroluminescent device of claim 17, whereinthe compound of Formula 3 is represented by any one of the followingFormulas 3-1 to 3-5:


19. The organic electroluminescent device of claim 2, wherein a workfunction of the cathode is at a HOMO energy level or less of the firstp-type organic material layer.
 20. The organic electroluminescent deviceof claim 2, wherein a difference between the HOMO energy level of thefirst p-type organic material layer and a LUMO energy level of the firstn-type organic material layer is 2 eV or less.
 21. The organicelectroluminescent device of claim 2, further comprising: a secondn-type organic material layer provided between the first n-type organicmaterial layer and the light emitting layer.
 22. The organicelectroluminescent device of claim 21, wherein the second n-type organicmaterial layer is doped with an n-type dopant.
 23. The organicelectroluminescent device of claim 21, further comprising: a thirdn-type organic material layer provided between the second n-type organicmaterial layer and the light emitting layer.
 24. The organicelectroluminescent device of claim 2, wherein the cathode is in contactwith the first p-type organic material layer.
 25. The organicelectroluminescent device of claim 2, wherein the first n-type organicmaterial layer and the first p-type organic material layer form an NPjunction.
 26. The organic electroluminescent device of claim 2, furthercomprising: a second p-type organic material layer provided between thelight emitting layer and the anode.
 27. The organic electroluminescentdevice of claim 26, further comprising: a fourth n-type organic materiallayer provided between the anode and the second p-type organic materiallayer.
 28. The organic electroluminescent device of claim 27, whereinthe second p-type organic material layer and the fourth n-type organicmaterial layer form an NP junction.
 29. The organic electroluminescentdevice of claim 1, further comprising: a substrate provided on a surfaceopposite to a substrate on which the organic material layer of thecathode or the anode is provided; and a light extraction layer providedbetween the cathode or the anode and the substrate, or on a surfaceopposite to a surface on which the anode or the cathode of the substrateis provided.
 30. The organic electroluminescent device of claim 1,wherein the organic electroluminescent device is a flexible organicelectroluminescent device.
 31. A display comprising the organicelectroluminescent device of claim
 1. 32. An illumination apparatuscomprising the organic electroluminescent device of claim 1.